1. Field of Invention
The present invention relates to stringed instruments which include a neck and finger board extending the supported strings away from the body of the instrument. More particularly, the present invention relates to a mechanism for correcting vertical and/or rotational misalignment in the neck of the stringed instrument.
2. Prior Art
Typical stringed instruments such as guitars, banjos, mandolins and other strummed instruments which have a significant amount of force applied to the neck of the instrument by reason of a plurality of strings in tension require accurate positioning of the fingerboard with respect to the array of strings. Such positioning is even more critical where frets are inlaid in the fingerboard to enable pitch selection for any selected string by depressing one or more fingers on a distal side of the fret from the resonating chamber or pickup part associated with the body of the stringed instrument. Although reference hereafter shall be made to an electric guitar, it will be apparent to those skilled in the art that the principles of this invention could be applied to other stringed instruments which share common construction design. Accordingly, further reference to the specific stringed instrument categorized as a guitar should be deemed to include other stringed instruments of comparable structure.
Proper alignment of the fingerboard of a guitar with respect to the suspended strings is essential. Although spacing and height displacement of strings from the fingerboard can be partially adjusted by the use of a specifically configured bridge or nut, it is preferred that the fingerboard of a guitar be essentially flat (meaning nontwisted) so that initial adjustments of the fingerboard position with respect to the rest of the instrument can be made in a predictable and controlled manner. In conventional fabrication of guitars, the neck is slightly bowed, further adjustments must be made to not only properly position the fingerboard with respect to the strings, but also to correct such misalignments. Such corrections are very difficult where the fingerboard is not initially flat, and compensation is virtually impossible when attempted from the outset for an extreme bow or twisted neck structure.
It has been reported that as many as 60% of the carved wood neck components prepared in typical fabrication procedures are simply discarded where initial misalignment is detected. For example, even though an artisan may start with a piece of hard wood which is straight and true in its rough form, as sections of the hard wood are cut away to form the tapering neck body, existent stresses within the wood may cause its configuration to slightly bow or twist. Such misalignment is unacceptable in finer instruments and typically results in the component being discarded.
Even where the neck structure remains acceptable after initial tooling, when applied to the guitar and subjected to stringed forces of 175 to 200 pounds compression, misalignment of the neck structure may result. Because of the unpredictable response of wood composition, guitar neck components cannot easily be prestressed to allow compensation for adjustments resulting from the described string pressure or loading which are imposed upon the neck.
Some adjustment has been facilitated by the use of a truss rod such as is illustrated in U.S. Pat. No. 3,396,621 or 4,557,174. The function of a truss rod is to redistribute loading forces imposed upon the neck to hopefully correct misalignment in the vertical bow which may occur with respect to the fingerboard and neck structure. It is important to note that the truss rod does not prevent loading of forces within the neck, but merely complements existing forces imposed by the strings to hopefully straighten or correct misalignment.
U.S. Pat. No. 4,432,267 illustrates a modular approach to providing for pre-strung adjustment in the neck component of the guitar by segmenting the neck and providing bolted attachment to the guitar body. Adjustment is accomplished by shifting the neck position with respect to the guitar body before tightening bolts which secure the neck to body orientation. This modular design has not provided the stability required for maintaining tuning nor for correcting other forms of misalignment. It is also cumbersome to adjust.
Furthermore, the prior problems of stress-imposed changes within the neck structure continue to be troublesome because forces arising from strings in tension can also affect distortion in the neck structure, particularly where weather conditions, heat and humidity might affect the wood. Therefore, a common impediment to construction and maintenance of a flat fingerboard and predictably straight neck body is the loading of the neck structure with the forces imposed by the tightly strung strings. Such stress may adversely affect any guitar in which string tension is applied to the neck in conventional manner.
In an earlier invention, the present inventors disclosed the use of a rigid, metal bar for relieving string tension from the supporting neck and fingerboard structure. This invention was described in U.S. Pat. No. 3,251,257, which explained that a rod could be inserted down a channel within the neck structure such that string tension applied at a distal end of the neck and fingerboard was loaded through the rigid bar into the guitar body. In this manner, the wood structure of the neck was not subjected to the severe tension and stress by reason of tightly drawn strings.
In addition, the referenced patent disclosed the use of a lifting force applied by contact of a threaded screw at the underside of the bar near the guitar body. For example, FIG. 2 of this patent illustrates adjustment screw 39 which is mounted at a support plate 39' and has its distal end contacting within a notch at the underside of the bar. This permits tension to be applied at one side of the bar as the screw is rotated inward, thereby countering the tension applied the strings 16. Accordingly, this earlier patent disclosed an adjustment mechanism which utilized the opposition of string tension versus bar tension in the vertical plane of the instrument to enable adjustment of the fingerboard and neck upward or downward. The limitations of such adjustment were controlled in part by the structural response of the neck material, the strings and string forces, and counter force established by the bar.
Although this mechanism provided improved adjustability along the vertical plane of the fingerboard, such adjustability was primarily limited to retracting the distal end of the fingerboard rearward by rotating the screw inward against the underside of the bar. Adjustments in the opposing direction were not as manageable because they depended upon the tension applied by the strings of the instrument. As guitar strings have become of lighter gauge, the difficulty of counter adjustments have increased.
In addition, the degree of abusive handling of instruments has greatly increased by virtue of modern performance styles, theatrics and attached hardware. For example, not only may a performance include swinging the guitar by its neck as part of performance choreography, but the use of tremolo bars and other hardware add greatly to the stress applied to the instrument, often resulting in mechanical misalignment of the fingerboard and neck structure.
It would therefore be beneficial to have an adjustment mechanism for maintaining and/or correcting alignment of the fingerboard of a guitar which does not depend on string tension and is capable of bearing stress applied in any form, whether it be by changes of weather, performance techniques or use of manipulative hardware associated with the instrument. Such progress would not only provide savings in the manufacture of such instruments, but would likewise reduce costs in correction of misalignment and difficulty of maintaining true pitch with respect to the strings of the instrument on a prolonged basis.